Rubber covered rolls are obtained by covering a metallic core such as an iron core with a compounded rubber and then vulcanizing and forming the compounded rubber, and are widely used in industrial machines in fields of iron manufacture, paper making, pulp, spinning, printing, plywood, etc. The performance of these rubber covered rolls varies depending upon machines in which they are used, applications intended, conditions for use and others, and rubber materials are selected according to desired conditions.
In general, chloroprene rubber (CR), acrylonitrile-butadiene copolymer rubber (NBR), styrene-butadiene copolymer rubber (SBR) and the like have conventionally been used widely as covering rubber materials for rubber covered rolls.
In recent years, speeding up of machines has however been attempted in various industrial fields such as iron manufacture, paper making and printing with a view toward improving productivity. With such speeding up, the conditions for use of the rubber covered rolls have also been changed to high temperature, high load and high-speed revolution. For this reason, covering rubber materials for rubber covered rolls have come to require good heat aging resistance, good mechanical strength properties and small heat build-up to repeated compression at a much higher level.
Further, in order to improve productivity, rubber covered rolls having a longer life have been required so as not to stop any production lines. For this reason, there has been a demand for developing a rubber material having good abrasion resistance and high tensile strength.
However, rubber materials having been used for covering materials to date encounter difficulties in producing any rubber covered rolls having good heat resistance, small heat build-up and long life. There have not been obtained under the circumstances any rubber covered rolls which can meet satisfactorily the recent demand level.
There are nitrile-containing highly saturated rubbers typified by hydrogenated NBR as heat-resistant and oil-resistant rubber materials. Although the hydrogenated NBR is relatively good in heat build-up and has abrasion resistance and tear strength improved more than those in NBR, it is still insufficient. Sufficient performance cannot hence be expected therefrom to use as a covering rubber for rolls.
In more recent years, it has been proposed to obtain a vulcanizate having excellent strength properties by blending a metal salt of an ethylenically unsaturated carboxylic acid with hydrogenated NBR (EP 344350). Such a vulcanizate is however insufficient in heat build-up. In addition, when the proportion of the metal salt is made higher to enhance the abrasion resistance and tear strength of a resulting vulcanizate, its adhesion to a metallic core is lowered even when an adhesive is used.